This question was at the heart of Kirtsaeng v. John Wiley & Sons (PDF), a Supreme Court case decided yesterday that has some big implications for our rights as property owners. Here’s the basic story: A guy named Supap Kirtsaeng bought some text books from Thailand, sold them to American students on eBay, and got publisher John Wiley & Sons really upset in the process.

Above: No, Woz — you can’t sell that.

The company’s argument? Objects purchased in foreign countries are not protected by the first-sale doctrine (which says that once you buy something, you’re free to do whatever you want with it) because first-sale only applies to things made in the U.S.

Because the Supreme Court has at least a modicum of common sense, it ruled against John Wiley & Sons, arguing that the first-sale doctrine says nothing about geography (which is true).

There are bigger implications here, though.

Think about it: If the courts prevent people from selling their foreign-made textbooks in the U.S., doesn’t that mean the law should also bar people from reselling their smartphones, computers, and cars — all of which are almost exclusively made outside the U.S.? (Americans imported $2.3 trillion worth of goods in 2011, says SCOTUS.) The consequences here are enormous, which is a big part of the reason why the Supreme Court voted 6-3 against Wiley & Sons.

Here’s the crux of the Court’s decision:

Thus, we believe that the practical problems that peti­tioner and his amici have described are too serious, too extensive, and too likely to come about for us to dismiss them as insignificant—particularly in light of the ever­ growing importance of foreign trade to America.

Dissenting opinion, led by Justice Ginsuerg, however, was largely dismissive of the Court’s hypothetical implications. “The Court’s parade of horribles is largely imaginary,” writes Ginsburg, arguing that manufacturers should have the right to prevent illicit importation of their products.

While the case has been settled, it does dovetail well with the ongoing debate over whether it’s legal for you to unlock your smartphone. To what extent is the thing you own actually yours? For a while it seemed as if we had answered that question, but the digital age is opening up the debate all over again.